A solid-propellant engine generally consists of a cylindrical outer body, more commonly known as an engine body, which is blind or open at its two ends, within which connecting materials, thermal protection and liner, for keeping the solid propellant in place within the body are disposed. The solid propellant forms the material which, when combusted, generates gases, the ejection of which through the nozzle is responsible for propelling the vehicle in which the engine is integrated.
As is known, in a solid-propellant engine as described above, the fuel may have two different designs, one being known as “cast-bonded”, illustrated in FIG. 1, in which the propellant 13 is secured to the body of the engine 11 and to its thermal protection coating 12 by way of structural connections brought about by the liner 14, the other being known as “free”, illustrated in FIG. 2, in which the propellant charge 22, previously crosslinked and inhibited, is kept in place within the engine body 21 by spacers 23 and 24 that define a gap 26.
The dismantling of a solid-propellant engine, that is to say its final removal from service, generally consists in reducing it to a configuration such that the function for which it was designed, namely propulsion, and thus the combustion of the propellant, can no longer be carried out. The main reason for dismantling is safety of property, and particularly of personnel, that may be in the vicinity of this engine even after it has been scrapped.
The dismantling procedure adopted, and also the means employed, generally meet various requirements, such as the simplicity of the operations carried out, or the guarantee of pyrotechnic safety (non-propagation of effects). They must also be in line with the dismantling rates imposed, that is to say with the quantity of engines to be processed during a given period of time.
The prior art proposes a number of dismantling methods which, however, are not able to meet the stringent requirements in terms of processing rates or in terms of simplicity of implementation. Simplicity of implementation is understood to mean in particular the absence of an operation of cutting the engine body or of emptying the propellant by any method.
The U.S. Pat. No. 5,220,107 granted to the company United Technologies Corporation on Jun. 15, 1993 refers in particular to the fragmentation of a bare propellant charge, by cooling the charge to a very low temperature and using a crusher or a press to fragment it.
The U.S. Pat. No. 5,025,632 granted to the company General Atomic on Jun. 25, 1991 proposes extracting the propellant from a cast-bonded engine having a central channel by means of a jet of cryogenic liquid. Such a method, derived from the principle of a hydraulic knife, is known to create non-negligible industrial cycle times and is thus incompatible with high dismantling rates.
The U.S. Pat. No. 5,552,093 granted to David E. Lee on Sep. 3, 1996 for its part claims a method for extracting propellant from an engine having a cast-bonded design, said method consisting in fully immersing the engine body in liquid nitrogen, while the charge is fragmented by application of repeated impacts. In addition to being expensive, such a method can also not be considered satisfactory from the point of view of pyrotechnic safety, the damaged propellant (which is cracked for example) generally having increased sensitivity to some attacks of the impact type.
The patent FR 03 08474 granted to the company SNPE Matériaux Energétiques on Aug. 19, 2005 describes a dismantling method based on successively carrying out steps consisting in the cutting of sections of engines and the cryogenic emptying of the propellant contained in each section, the fragments of propellant being subjected, after a possible crushing operation, to a final processing operation consisting of biological processing of the perchlorate residues that form the (dissolved) liquid effluents, these residues having previously been freed of (non-soluble) organic and metallic species that enter the composition of a composite propellant.
However, such a method has a lengthy cycle time. It also forms a costly solution since it makes use of numerous cutting and emptying operations. It is furthermore relatively complex to implement, since it makes use, for the recycling of the propellant, of technology employing living organisms (population of bacteria), the activity of which affects the processing efficacy. On account of its biological nature (use of living organisms), it is also very difficult to control, and this can lead to significant constraints in the scope of high dismantling rates.
Such a method employing processing of the biological type furthermore has use limitations since, to date, it is only suitable for processing water-soluble chemical compounds such as ammonium perchlorate, an oxidizing charge mainly employed in the production of composite propellants. Consequently, it cannot be employed to dismantle conventional (solventless and cast) “double base” solid propellants or advanced propellants such as XLDB, NEPE Azorgols. In particular, it does not satisfy the problem of dismantling tactical missile engines, most of which, for reasons of discretion, incorporate homogeneous propellant technologies.